Apparatus for making high-frequency cable joints



Feb. 14, 1950 L, WETHERILL 2,497,708

APPARATUS FOR MAKING HIGH-FREQUENCY CABLE JOINTS Original Filed Feb. 21, 1945 2 Shets-Shoet 1 e @f Pig-1- Q /'rec/o/y of %y`\ o A fave f/-avf/ 263 24 V h,- Kal/17A 34 iV/ll/I/ IIA f Figa 6 a 7 V 7l Inventor: 1.5mm Wethevill, by Mc?. /BMZZL H i5 Attoney L. WETHERILL Feb. 14, 1950 APPARATUS FOR MAKING HIGH-FREQUENCY CABLE JOINTS 2 Sheets-Sheet 2 Original Filed Feb. 2l, 1945 LEE/TER LINE or CABLE AIR -b kes/WER Lm: of CABLE Inventor: Lgnn Wetherll, bg Ma. M

H Attorrweg.

Patented Feb. 14, 1950 APPARATUS FOR MAKING HIGH- FREQUENCY CABLE JOINTS Lynn Wetherill, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application May 15, 1946, Serial No. 669,857, which is a division of application Serial No.

578,965, February 21, 1945.

Divided and this application September 29, 1947, Serial No.

3 Claims.

My invention relates to electric cable joints in the form of connectors for making joints between lengths of various types of cable. More specilically, the invention relates to apparatus for con- `structing connectors for cables which are particularly adapted for the transmission of high frequency currents of the order of several hundred megacycles. This application is a division of my copending application for Apparatus for making high-frequency cable joint, Serial No. 669,- 857, filed May 15, 1946, which is a division of my copending application for Electric cable and cable joint, Serial No. 578,965, iiled February 21, 1945, and assigned to the same assignee as the instant application.

My invention is of particular interest in connection with cables having solid dielectric medium between the inner and outer conductors in which lengths of the cable are connected to other cables by means of connectors employing different dielectric medium from that used in the cable. Sometimes joints using a solid dielectric medium may be used but usually the medium is gaseous, such as air. One advantage of using air as the dielectric medium at the cable joint is that it permits quick assembling and dismantling of such cable connections in field use. At the same time, the connection or joint between .cable sections must be so constructed that the separable parts thereof may be quickly and easily attached to lengths of cable cut from bulk stock.

It is of particular importance in cable lengths used with high frequency currents that the characteristic impedance, or surge impedance, of the cable be uniform throughout its length irrespective of variations in the dielectric media used in adjacent sections of cable, and in the joints connecting these sections, and irrespective oi variations in the diameters of the inner and outer conductors. Such variations in diameters almost invariably occur at points where joints are placed in the cable length in order to secure uniform breakdown strength in the dielectric medium.

The requirement of constant surge impedance alone will not suiiice to give highest eiiiciency in a high frequency transmission line incorporating joints. I have found that it is also important to so construct the cable joint that no reflection of the high frequency waves occurs at faces between different dielectric media, particularly where the diameters of the inner and outer conductors have been changed as at the cable joint. Otherwise, spurious or unwanted standing waves may result with consequent loss of power in the trans- 'mission'line It is an object of my invention to provide a, new and improved apparatus for making a cable joint of the type described.

In the accompanying drawing, Fig. 1 illustrates a cable and a joint therefor constructed in accordance with my invention; Figs. 2 and 3 illustrate successive steps in the method of forming the cable joint; Fig. 4 illustrates a modication of the cable forming method; Fig. 5 illustrates apparatus for carrying out the method accordiing to my invention; Fig. 6 is an exploded View of parts of the apparatus of Fig. 5; and Figs. 7, 8 and 9 are diagrammatic views illustrating the principles by which electricenergy is transmitted through a high frequency cable and joint constructed according to my invention.

It is well known that the characteristic impedance, or surge impedance, Z of an electric cable or of any small part thereof may be expressed as L=inductance in henries per unit length Czcapacitance in farads per unit length QI bl in which This term may also be expressed as in which From this formula, it `will be seen that the characteristic impedance of the cable is a function of three variables k, R and r. If any one of these variables is changed, a corresponding change will `be necessary in the remaining `variables if the characteristic impedance of the cable is to be main-tained constant throughout its length.

In 4cases where it is desired to utilize cable joints 'having separable connectors for taking lengths of cable apart, provision must be made for connecting together the inner and outer conductors of the cable length. This means that some form of connector must be fastened to the inner conductor. l'll'most invariably'the connector is of a diameter greater than that of the inner lconductor `ofthe .high vfrequency cable. Furthermore, .it is highly desirable to employeJ gas 'insu- :seme

is to be followed throughout the entire length of the cable, including the cable joints, variations in the size of the inner and outer conductors will occur at the cable joints and also the spacing between the conductors will vary because the dielectric constant of the insulating medium be tween the conductors has been changed.

In the form of my invention illustrated, I have shown a coaxial high frequency cable in which a solid dielectric medium is employed, such as polyethylene. This material has a dielectric constant of about 2.4. Furthermore, I have chosen to illustrate such a cable as being pron vided with connectors forming a cable joint in which air is utilized as a gaseous dielectric rnedium between the inner and outer conductors. The dielectric constant of air is 1. Since the dielectric constant of air is less than that of polyethylene, the ratio R/ in the joint must be smaller than for the cable. Since dielectric strength of air is less than that of polyethylene, the spacing between the conductors at the joint Imust be increased in order not to lower the overall dielectric strength of the cable. However, the diameters of the inner and outer conductors of the cable have been so chosen in relation to the dielectric medium as to make the charac- `teristic impedance of the joint substantially equal to that of the cable. In order to match the characteristic or surge impedance of the joint to that of the cable, and in order to connect the large diameter conductors of the joint to the relatively smaller conductors of the cable, a portion of the joint is formed with tapered conductors so that the diameters and spacing of the conductors of the cable are gradually increased to those of the joint. This arrangement is shown by Fig. 1.

Although the characteristic impedance of the joint has been matched to that of the cable, this requirement alone is not sufficient to attain maximum eiiiciency in the transmission line. It is also important to so construct the cable joint that no reflections of high frequency waves occur as the wave passes down the cable. Heretofore, the dielectric medium in the cable has vbeen terminated abruptly whenever the cable has been connected to a joint having a different dielectric medium. This has almost invariably resulted in reflection of part of the wave in those instances in which there is a change in the diameters of the inner and outer conductors at cable joints. I-Iowever, I have found that the interface between the two dielectric mediums of the cable and joint may be so positioned as to substantially preclude reflections of the high frequency wave and at the same time give a substantially constant surge impedance at the joint. The wave is refracted so that it passes from one dielectric medium to the other with substantially no reflection. The arrangement is particularly useful in those instances in which the diameter of the cable joint varies from that of the cable and in which tapered conductors are used in the joint to obtain a uniform characteristic impedance of the transmission line.

In Fig. 1 of the drawing, I have shown a cable and joint therefor in which a portion of the solid dielectric of the cable has been extended up into the cable joint and terminated at an interface or boundary disposed at an angle. This angle is critical. It depends upon the dielectric constants of the insulating materials used in the cable and joint. It is so located as to keep the characteristic impedance of the cable substantially constant through the joint as Well as precluding reflections of the high frequency Wave. In order to more fully explain the manner in which the angle of the boundary is determined, I have shown the arrangement of the dielectric media and boundary in the diagrammatic views of Figs. 7 and 8.

In Fig. 9, the high frequency wave is represented as parallel lines moving along the paths of the dielectric media. It remains as nearly as possible perpendicular to the boundaries formed by the conducting surfaces. The wave is shown moving along the solid dielectric until it reaches the boundary where it is refracted as it passes into the gaseous dielectric medium. As mentioned above, the boundary angle is critical in order to secure proper refraction of the Wave. In order to illustrate the boundary angle, a small portion of the wave front and boundary angle, as indicated by the dotted lines in Fig. 8, have been shown in the enlarged schematic view of Fig. 7.

Fig. 7 illustrates the boundary plane separating the two dielectric media which are indicated by the parallel dotted lines. The dotted lines also represent the path of the high frequency wave. In Fig. 7,

B--angle of incidence of the wave v A=angle of refraction of the wave.

It is assumed that Vizvelocity of wave in insulating material entering boundary V2=velocity of wave in insulating material leaving boundary.

By the sine law of refraction V2 sin A lsin B Since the velocity of an electric wave is inversely proportional to the square root of the dielectric constant 1 V JK.

where K1=dielectric constant of insulating material on entering side of boundary (side of incidence).

2 vK. y where K2=dielectric constant of insulating ma# terial on other side of boundary (sideof refraction).

Thus, it is seen that to secureproperrefracf their rtion ofthe wavethe angles A and B are deter-l mined by the lsquare root of the ratio of the di electric constants for the insulating materials usedxonv each side of the boundary.

In meetingthe requirement for constant surge imlpedanoevon each side of the boundary, reference fismade to the formula for surgey impedance already 'mentioned in which Fromfthis equation, it will be apparent that the surge impedance Z is inversely proportional to lntwhich r=theradius of the inner conductor r+t=the radius of the outer conductor.

Asangle Ain Fig. 9 grows smaller and smaller, the volume of dielectric material contained in the f. angle will approach a` `rectangular prism. The angleA includes adength a` on the circumferenceof circle having `radius r so thatthe surge impedance of the volume in angle Aris Since the quantity 120W isV aV constant By comparing Figs. 9- and 7, it will be apparent tliatthev distance t in Fig. 9 corresponds to GF in-Fig. 7. Assuming that Z1=surge impedance .on the enteringside of `Vthe boundary Zi=surgeinrpedance onthe opposite side:4 of the boundary.

t DE

Since for constant surge'imipedance cos B V K cos A and for proper refraction of the wave K sin A these two equations may be solved simultaneously to incorporate both factors in determining-the ultimate values of angles A and B. Thus r 922 sin A cosA sin B By trigonometry cos A= 45 (Equation `1) 50 Substituting Equation 1 1 .time w n A:

5 But bythe previous. equationv cos B VKz-cos A Comparing the two equations` This solution gives values for angles A and -B such that Thus it will be seen that the boundary angle is determined by the ratio of the dielectric constants of the insulating materials on each side of the boundary. For the special case in which air, having a dielectric constant of 1, is used on one side of the boundary the expression N/ Il y K2 -In the showing of Figs. 1, '7 and 8, and in the mathematical steps set forth above, the electric wave has been considered as passing from a solid dielectric medium into a gaseous one. This has been done in the interest of simplication and to make the functions of the boundary more clearly apparent. Howevenit should be realized that the electric wave also travels in a reverse direction, i.e., from the gaseous to the solid dielectric medium. In such instances, the angles A and B in the equations mentioned above would be reversed. Similarly, Z1 and Z2 would be reversed as would K1 andKz.

Turning now to the actual construction of my invention shown by Fig. 1, two cable sections I and 2 are joined together with -a connector 3. Each cable section has an inner conductor 4 and an outer conductor 5, in the present instance made of braided material and concentrically spaced from the inner conductor 4. The annular space between the conductors is lled with insulating material, in the present example, a solid dielectric 6, such as polyethylene. The outer conductor is protected by a jacket 'I made from suitable material such as polyvinyl chloride.

The connector 3 for connecting two cable secbecomes since K2: l

.tions I and 2 is made up of two terminals and includes means for securing and electrically connecting such terminals together. vEach terminal comprises a casing 8 which has a substantially cylindrical end portion 9, a'substantia-lly conical or tapered intermediate portion ID and a substantially cylindrical end portion I I. The cylindrical casing portion 9 forms a packing chamber to receive the severed end of the cable. A braid clamp AI2 is located in said chamber between an outwardly turned portion of the braided outer conductor and the jacket 1. The jacket 'I is securely sealed to the casing 9 and the outer conductor 5 is securelyconnected to the casing 9 by means of suitable packing rings I3 and washers I4 held in position by a gland nut I5 threaded into the casing 9. In this Way, the outer conductor 5 is electrically connected to the joint casing 8. *l

The inner conductor 4 within the end casing I I carries a metallic cone I6 which has its apex near the casing portion 9 and its base within the cylindrical casing portion I I. The surface of the cone is roughly parallel to the inner surface oi conical intermediate portion I0. Together these elements form tapered surfaces for maintaining approximately uniform surge impedance through the joint as the small diameter conductors of the cable merge with the larger ones of the joint. The metallic cone I6 has an extension I1 with a threaded collar I8. The cone is secured to and electrically connected with the conductor 4 by:

any suitable means such as solder I9 lllng an opening in the cylindrical portion I'I. A sleeve 20 is threaded at one end to the threaded collar I8 ci the cone I6. Each of the two terminals on the two lengths of cable to be connected together has the elements It to 2t described above. The sleeves 29 of the two terminals areelectrically connected. by means of a connecting memberll which has an end portion 22 disposed within one of the sleeves 2! and preferably brazed or fused thereto. The connecting member 2l has an intermediate portion or collar located between and forming abutments for the adjacent ends of the sleeves 2t of the terminals. The connecting member in addition has a slotted cylindrical portion 23 forming a snug iit in the other of the sleeves 2t so that a good electrical connection is obtained between the sleeves, p

The casings 8 of the terminals are electrically and mechanically securely connected together by a suitable coupling. In the presentexample, the casing il of the left-hand terminal is provided with a flanged extension 26 secured to the casing by suitable means such as solder 25. The 4.casing 3 ci the right-hand terminal` is provided with another flanged extension 26 suitably secured to the casing. The flanged extensions are sealed together by means including a packing ring 21 and a flanged nut 28.

The solid dielectric 6 has a conical end face or boundary 29 and is held in position in tight sealing engagement with the outer conductor or casing by means of a sealing gasket 3B engaging the outer end portion of the solid dielectric and held in position by a retaining ring 3l. The retaining ring itself is held in position by a spunin projection 32 oi the casing. The sleeves 20 of the two terminals and the intermediateportion of the connecting member 2| form a substantially continuous cylindrical surface concentric within the inner cylindrical surface of the end portions Il and the flanges 24, 26 of the terminals, the latter constituting part of the outer conductor. Preferably, the annular space 33 formed between the inner and outer conductors of the connector 3 is lled with a gaseous dielectric such as air. However, it will be apparent that other gases may be used, such as nitrogen. Also in certain instances, the space 33 might be lled with insulating compound having high dielectric strength, for example, polystyrene.

As aforementioned, the boundary surface 29 makes an angle with the dielectric media of the cable and joint such that As shown by 1, the angles A and B are measured from a line normal or perpendicular to the boundary line 29 of the solid dielectric material. 'Ihe solid dielectric as far as it engages directly the cylindrical conductor 4 has a constant inner diameter. Adjacent the Imetallic cone IB. the diameter of the solid dielectric increases gradually and reaches a maximum at or near the base of the metallic cone le. In other words, the inner surface of the solid dielectric is substantially conical within the cable connectoror vterminal and has a tangent approach to the cylindrical inner surface oi the solid dielectric in the cable section. The outer surface of the solid dielectric in the connector is likewise substantially conical with slightly curved contour and a diameter increasing toward the end of the cable. The inner and outer curvatures of the solid dielectric should as` small@ as.V possibles Practicalconsiderations limit the length cfs theconical surfaces. The outer diameter'of the inner cylindrical conductor andy the inner diameterv of the outer cylindrical conductor of theconnector are chosen to produce with the chosenv dielectric a. uniformisurge impedance equal tofthatof the solid cable section.

Ifani electric waveisconsidered approaching the' boundary, from thesolidfside, it is desirable, from a. theoretical standpoint, that the wave approach; the boundary at the. angle of incidence B, as indicated in the diagrammaticshowing of,v Fig-.H 7.'. If` this` were to happen, it would mean that' the contours, of,l the inner and outer cones of:` the concentric conductors shouldf approach? thefboundary` at` the same` angle in order tocause: theeleotric wavetoapproach at the` desired'angle. However, from a` practical standpoint, it is not possible: to have.` both` the inner andY outer cones approachtheboundary;v at the` same `angle becauseV considerations ,ofy substantially constanty surge im-` pedance require that the two curves of the lcones diverge. Although it;Y is necessary to. make the cones diverge,v it` isy possible to reduce-the'unde-- sirable effect of the divergence by makingethe-two conesdiverge fromthe desiredangle. of incidence by equalaamounts and: in opposite directions so that they average of the directions of the.` two cones: will be` substantiallyy correct.v This would meanthat; thexaverage angle of. incidence of an electric i wave: would: beA correct. TheV cable joint thusifar described. islconstructed by the." new and improved method and apparatus comprising my invention.

During manufacture: of. a cable joint; or terminal,l according to-my invention, thev jacket. 1.5 is stripped back from therend. pcrtionof' a cable (Eig.y 22).. rIhereupon thev glandnut l5, washers I4?. and gaskets I3* arer passed? over the jacketI l and the braid.. clamp l2 i'spassed over the'outer conductorf and awedgedi under thexjacket' le The braid' 5; formingthe` outerlfconductor ofi theMcable-,f is then turned outwardly to formaangesaround thevbraidtclampf l 2: The. lcasing '8111s. then passed oversv the cableiendportion; Theglandnut l5. is tightened. to lfo'rmf'. a' weathereproof sealr between the casin'gszfandlthe jacket-lof the c'ablesection'.` In: thev present. instance@ the: innerl conductor.V 4y andthe solid..v dielectric 6-y ony thewen'd portion :eX- tleridi.axially` beyond the` casing. 8; Thefterminal parts thus' farassembledare then: placedintoa molding pressitolmold the dielectric material -on the end .portion ,into the: desired shape.V

The press to accomplish this, assh'own' in part iniEig. 2 andiin fulliin Fig. 5; comprisesua cylinder Nfl-forming a moldingch'amb'er.' Aninlet'fchannel 35r1connected toa pipe 36 and anexhaust 4port 321,1. permits aaheating medium, such as` hotair, to be .-circulatediin' the cylinder 34 lduring the moldingrA operation. The-cylinder- 34A hasa threaded end portion` mounted ona supporting plate- 38 andforming aninnerk annular shoulder 39'A Y The supporting plate 38. isi connected tofan' end plate 40.1(Fign51) by means of four rods 4|. A plunger 42 is slidable into the right-hand end of the cylinder 34 and has' an end face' which conforms to the predetermined shapeof the boundary or end face 29 (Fig. 1) to be producedf Thev plunger has a Ventchannel MY for discharging gases as the plunger passes beyond the exhaust opening 31 and for discharging some ofthe molded dielectric compound'during the molding operation (Fig. 3), for apurpose to be describedlater.

A'sshown by Figure 5, the right-handendiof the plunger is secured to a threaded sleeve 45. anda plate46 slidably engaging the rods 4I and acting as a; guide for the plunger on said rods. The plunger is actuated, that is, moved axially by means of a screw 4l connected at its righthand. end to a handle 48 and having screw engagement withtheend plate 4U. The left-hand endrof the screw 4.1 has a head 49 supported within the sleeve 45 by means of a ball-bearingl 50 and isloosely connected to the plunger 4`2by a slidable cup 5l andacompression spring 52. Upon clockwise rotation ofthe handle 4 8 the screw 41 is moved toward. the left. This movement is transmitted throng-hV the. spring 52 to the plunger 4'2. The spring. normallyv acts as a shock absorber to effect uniform. transmission of force from the screw tofthe cylinder. As theresistance to Inovement ofthe plunger increasesfduring the molding operation the spring is compressed until the cup 5| engages directly the end face of the plunger 42, the spring` thenV being completely enclosed within a bore inthe plunger.

The left-hand end of theplunger 42u has a shoulder 53 for supporting the base of the Inetallic cone I6. In some instances it maybe desirable to use a special steel cone of same-shape as. the cone I6 for the moldingoperation. During the molding operation a cone i6 is insertedY into thev end of the plunger and a cable with a terminal casingris assembled on the tool as shown in Figs. 2 and 5. The casing 8 of, the terminalis then seated against theshoulder 39 of the cylinder 34.-

As shownin the exploded View of Fig. 6, the molding press includes means for clamping in positiony a cable with a terminal casing thereon. This meansincludes a cylinder 54 having. a threadedl portionsecured to. an anchor plate 55 held on the supporting plate 38A by means of two spaced rods 56. The cable projects centrally through the cylinder and is engaged by means of a threepart clamp 5l bearing against thrust platef58 provided with a conical opening59. The thrust plate is seated against the right-hand end of the cylinder 54 and hasan opening 60 for accommodatingone of the rods 56 and a `recess 6l for accommodating the other rod 56. The rod 56v projectsthrough the opening 60 ofthe thrust plate and constitutes a pivot for the latter; that is, the thrust plate may be swung into position about the rod 56 so that the other rod 56 slips into recess 6I.

During assembly a-cablerwith a terminal casing thereon is inserted through the cylinder 54. Thereupon the three parts of-theclamp 5l are positioned4 about the cable. Then the thrust'plate 58 is moved into positionto support the clamp and nally the threaded cylinder 54 is rotated toward the thrust plate 58 in order to force the thrust plate 58- uparound the clamp which, in turn, engages the terminal casing.

During constructionof the joint, it isdesirable to strip the cable ina manner such that the amount of compound-left onthe end portion is sufficient to-produce the enlarged conical end portionof the dielectric. In-some caseswhere the volume ofV compound on the end of the conductor is notsuflicient, additional compound may beplaced into thecasing in the form of-a ring or insulation pellet 62.as shown in Fig. 4. This additional compound is to be of the same dielectric material as thatonuthe cable.-

yDuring the moldingoperation, hot air or like heating medium, is admitted through the pipe 36 to the cylinder 34 t'o heat the insulation until it 11 reaches a certain temperature, for example, 110 C. in case such insulation or dielectric is made from polyethylene. Thereupon the plunger 42 is slowly advanced by rotating the handle 48. As the plunger advances, the cone I6 peels back the dielectric medium on the cable, and together with the angular end face 43 on the plunger, forces the insulation into the tapered section l of the terminal casing.

Although the molding press and the dielectric compound on the cable are heated during the initial stages of the molding operation, it is important that the dielectric compound be completely cooled upon completion of the operation. This is so because the dielectric, such as polyethylene, contracts upon cooling and it is extremely important that there be no voids in the dielectric compound after it has been molded into position. For this reason, during the latter stages of the molding operation, the terminal and molding press near the cable end of the construction are cooled by means of a water bath.

Since the dielectric compound shrinks on cooling, it is important for the operator to know whether or not the plunger of the molding press is being moved fast enough to make up for any shrinkage in the compound to prevent the formation of voids. This is the purpose of the channel 44. As the plunger is advanced, compound is forced out through the passage 44, in the manner indicated by Fig. 3. If the excess compound were allowed to creep out of the molding press along clearances between the plunger 42 and the cylinder 34, the operator would not be sure that the plunger was being advanced at the proper rate because a considerable amount of the dielectric compound might accumulate out of sight in the space between these two members. However, by providing the channel 44, the operator can immediately ascertain whether or not the plunger is being moved at the proper rate because the excess compound is always visible.

During the molding operation, the operator should move the plunger 42 fast enough so that material is continuously extruded through the channel 44 during the entire molding cycle. Moreover, it will be apparent that the rate at which material is extruded out of the channel 44 will give the operator an indication as to whether or not the plunger is being moved at the proper speed. If the plunger is moved too fast during the initial stages of the molding cycle, then an excess of dielectric compound will be extruded through the channel 44 giving an indication to the operator to decrease the speed of the plunger. On the other hand, during the latter stages of the molding cycle when the dielectric compound is being cooled down and shrunk, if no compound is extruded through the channel 44, then the operator will know that the plunger 42 is not being advanced fast enough. Under ideal conditions, the press should be operated in such a way that the plunger reaches its final position at a time when the insulation has become thoroughly cooled and shrunk and the plunger should be operated so that the dielectric compound is extruded through the channel 44 continuously during movement of the plunger. When this procedure is followed, it is practically certain that there will be no voids in the molded insulation of the terminal.

Upon completion of the molding operation, the terminal casing is removed from the press and the gasket 30 is inserted together with the retaining ring 3|. The gasket 30 is held in position by application of pressure on the retain? ing ring and then a projection is spun in the cylindrical casing 8 to hold the retaining ring 3| in position. The projection 32 may be formed by rotating the terminal casing on a mandrel. Alternatively, the terminal casing may be held fast and a suitable forming tool rotated around the periphery of the casing. Finally, the metal cone I6 is secured to the inner conductor by any suitable means such as the solder I9. Then the coupling member 24 or 26 is fastened to the terminal casing 8.

Thus, with my invention I have accomplished an improved apparatus for making cable connectors in which reflection of high frequency waves in the cable is substantially eliminated and whereby the characteristic or surge impedance remains substantially constant throughout the cable lengths and joint. The method of attaching the connectors to the cable is one which may be performed equally as well in the field as in the factory. Connectors constructed in accordance with my invention are simple in construction and are especially suitable for making joints in field use.

While I have, in accordance with the patent statutes, shown and described a particular embodiment of my invention, other changes and modifications will be obvious to those skilled in the art and I, therefore, aim in the appended claims to cover all such changes and modiiications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A tool for `forming cable connections comprising a cylinder having an inlet for heating medium and an exhaust, a plunger with a conical end face slidably extending into one end of the cylinder, means for actuating the plunger to force it into the cylinder, and means for supporting a cable section with a terminal on the other end of the cylinder.

2. A tool for forming cable connections comprising a cylinder having an inlet for heating medium and an exhaust, a plunger with a conical end face slidably extending into one end of the cylinder, means for actuating the plunger to force it into the cylinder, and means for supporting a cable section on the other end of the cylinder, said plunger having a ycentral recess in its conical surface for supporting a metallic cone and a vent in its wall through which molded material may be extruded.

3. A tool for forming cable connections comprising a cylinder, means for supporting a cable section on one end of the cylinder, a plunger extending into said cylinder from the other end and being adapted to mold compound around the cable section, said plunger being provided with an opening therein through which part of the molded compound is extruded as the plunger is moved toward the cable section.

LYNN WETHERIIL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 369,595 Drescher Sept. 6, 1887 2,135,380 Benge Nov. 1, 1938 2,163,798 Mucher June 27, 1939 

